Stainless steel alloys of high chromium-nickel type are commonly used for components employed in nuclear fission reactors due to their well known high resistance to corrosive and other aggressive conditions. For example, nuclear fuel assemblies, neutron absorbing control devices, and neutron source holders are frequently clad or contained within a sheath or housing of stainless steel of Type 304, or similar alloy compositions. Frequently such components, including those mentioned, are located in and about the core of fissionable fuel of a nuclear reactor where the extremely aggressive conditions such as high radiation and temperatures are the most rigorous and debilitating.
Commercial solution or mill annealed stainless steel alloys are generally considered to be essentially immune to intergranular stress corrosion cracking, among other sources of deterioration and in turn failure. However, stainless steels have been found to degrade and fail due to intergranular stress corrosion cracking following exposure to high irradiation such as is typically encountered in service within and about the fissionable fuel core of water cooled nuclear fission reactors. Such irradiation related intergranular stress corrosion cracking failures have occurred notwithstanding the stainless steel alloy having been in the so-called solution or mill annealed condition; namely having been treated by heating up to within a temperature range of about 1,850.degree.to 2,050.degree. F., then rapidly cooled as a means of solutionizing carbides and then deterring their nucleation and precipitation from solution out into grain boundaries.
It is theorized that high levels of irradiation resulting from a concentrated field or extensive exposure, or both, are a significantly contributing cause of such degradation of stainless steel alloys, due among other possible factors to the irradiation promoting segregation of the impurity contents of the alloy.
Past efforts to mitigate irradiation related intergranular stress corrosion cracking in stainless steel alloys comprise the development of resistant alloy compositions. For example, stainless steels containing low levels of impurities have been proposed.